Claire FOURMENTIN PhD defense

Développement d'optiques à GRadient d'INdice de réfraction (GRIN) par échange ionique pour des applications à l'imagerie thermique dans le domaine 8-12 µm
Claire FOURMENTIN PhD defense

Thursday December 15, 2022 - 10:00

Beaulieu Campus, Rennes
Building 10 B, Grandjean Amphitheater

Glass & Ceramics team



This PhD work focuses on the development of Graded Refractive Index (GRIN) optics in chalcogenide glasses transmitting in the infrared between 8 and 12 µm. Ionic exchange is a well-known and industrialized process for the creation of GRIN optics in oxide glasses, but only few tests have been performed yet in infrared transparent glasses. First, we tried to optimize the Na+/K+ ion exchange in nitrate baths with the chalcogenide glasses (0,72 GeSe2 – 0,28 Ga2Se3)75 (NaI)25 in order to obtain a reproducible maximum diffusion depth and to understand the mechanism. The maximum depth of 2 mm obtained in 40 days allowed us to make a 4 mm diameter moldable converging GRIN lens with a Δn = 4.5x10-2 and a polynomial index profile. This is the first chalcogenide glass GRIN lens made by ion exchange. The optical interest of such lens has been demonstrated thanks to optical designs and simulation realized in collaboration with ONERA. Ion exchange also allows to obtain preforms with a  refractive index gradient  which, once fibered, could allow to obtain GRIN fibers.

In a second step, we were interested in the optimization of the ion exchange process involving Ag+ ions. Indeed, Ag+ ions have the particularity to migrate rapidly in glasses and allow to obtain diffusion depths of the order of a millimeter in only a few hours. The maximum index difference that can be obtained with these exchanges is of the order of 10-1, ten times higher than for a Na+/K+ exchange. A divergent refractive index gradient created by solid/solid Na+/Ag+ ion exchange was obtained in the glass (0,72 GeSe2 – 0,28 Ga2Se3)75 (NaI)25, demonstrating the high potential of this promissing process.


Andréa PIARRISTEGUY, Maitre de conférences, ICG, Université de Montpellier, Rapporteure
Marc DUSSAUZE, Chargé de Recherche CNRS, ISM, Université de Bordeaux, Rapporteur
David LE COQ, Professeur des universités, ISCR, Université de Rennes 1, Examinateur
Guillaume DRUART, Maitre de recherches, ONERA, Université Paris-Saclay, Examinateur
Yann GUIMOND, Directeur Général, UMICORE IR Glass, Invité
Sylvie PAOLACCI-RIERA, Responsable du Domaine Scientifique Photonique, DGA, Invitée
Philippe ADAM, Membre de la Société Française D'Optique, Invité
Xiang-Hua ZHANG, Directeur de Recherches CNRS, ISCR, Université de Rennes 1, Directeur de thèse
Laurent CALVEZ, Professeur des Universités, ISCR, Université de Rennes 1, Co-directeur de thèse


Xiang-Hua Zhang, xiang-hua [dot] Zhangatuniv-rennes1 [dot] fr
Laurent Calvez, laurent [dot] calvezatuniv-rennes1 [dot] fr